This invention relates to the enzymatic hydrolysis of cellulose to obtain water-soluble sugars.
There has been considerable interest in the development of a process which will take advantage of the natural abundance of cellulose and the mild reaction conditions utilized in enzymatically hydrolyzing or saccharifying cellulose to simple sugars such as glucose. For example, Ghose, U.S. Pat. No. 3,642,580, discloses a saccharification process wherein a concentrated cellulase enzyme solution is employed to hydrolyze finely divided dry cellulose to obtain a cellulose-cellulase-sugar slurry which is then subjected to ultrafiltration under pressure to separate the sugar syrup from the insoluble cellulose and soluble enzyme components, thereby allowing reuse of the enzyme. Mandels and Kostick, U.S. Pat. No. 3,764,475, disclose a similar process which eliminates the ultrafiltration step of Ghose by continuously adding dry cellulose during hydrolysis to immobilize the cellulase enzyme by adsorption on excess unhydrolyzed cellulose. More recently, in an article appearing in Biotechnology and Bioengineering, Vol. XVI, 1471-1493 (1974), November, 1974, Mandels, Hontz and Nystrom report on the use of pure and waste cellulose from various sources as a substrate for enzyme production and for enzymatic saccharification. It appears from these references that it has been considered necessary to separate the cellulase enzyme from the milieu in which it is produced prior to its use in hydrolyzing cellulose.
Toyama et al, Proc. IV IFS: Ferment. Technology Today, 743-757 (1972); report on the feasibility of producing sugars by the enzymatic saccharification of cellulosic wastes utilizing Trichoderma viride cellulase. On pages 753 and 754, there is disclosed the elaboration of enzyme in solid cultures on trays (Japanese koji type culture) and use of the entire solid culture so obtained as the enzyme source in a subsequent enzymatic saccharification of delignified cellulosic substrates. There is also disclosed the use of an aqueous extract of the enzyme from the same solid cultures in saccharifying the same delignified cellulosic substrates. Table 23 on page 753 shows the results obtained using the entire solid culturs. Table 24 on page 754 shows the results obtained using the aqueous enzyme extracts from the solid cultures. A comparison of Tables 23 and 24 with respect to the yields of sugar obtained shows that one solid culture, rice straw, gives lower yields than use of the aqueous enzyme extract from the same solid culture; with the other solid culture, rough printing paper, the reverse was true.